Ken Clarke has brushed aside judicial opposition to the UK's proposals for reforming the European court of human rights, claiming that the "Brighton declaration" by 47 member countries would result in fewer cases being appealed to Strasbourg.

Dismissing criticism by the British judge Sir Nicolas Bratza – the court's president – the justice secretary insisted the declaration would speed up the process of tackling the backlog of more than 150,000 cases waiting to be heard.

Clarke did concede there had been opposition from other states within the Council of Europe and not as much progress had been made as the UK originally hoped. "These reforms represent a substantial package and are a significant step towards realising the goals that the prime minister set out in Strasbourg,"

Speaking in Brighton following agreement on the text of the declaration which has been refined over months of negotiation, Clarke said: "Taken together, these changes should mean fewer cases being considered by the court. Those that it considers should be allegations of serious violations or major points of interpretation of the convention and will be processed without the scandalous delays we are seeing at present.

"I'm a lot less relaxed than Sir Nicolas about the progress already being made before [this] declaration."

Sir Nicolas Bratza had earlier criticised UK methods for reforming the Strasbourg court and called for more funds to tackle the massive backlog of cases.

Addressing the Brighton conference, the president of the ECHR welcomed the fact that UK attempts to narrow the criteria for admissibilty of cases had been substantially deferred.

His comment took some of the gloss off the government's triumphal presentation. The UK currently holds the rotating chairmanship of the Council of Europe and has been pushing its reform agenda aimed at ensuring that fewer cases are decided in Strasbourg and more in British courts – a policy known as "subsidiarity".

Bratza questioned the need for many of the UK-backed reforms. "We have difficulty in seeing the need for, or the wisdom of, attempting to legislate for [subsidiarity] in the European convention of human rights, any more than for the many other tools of interpretation which have been developed by the court in carrying out the judicial role entrusted to it," Bratza said.

"We welcome the fact that no proposal for a new admissibility criterion is now made in the declaration and we are grateful for the efforts to take on board the court's concerns in this respect … It is [already] the court's practice to reject a case as inadmissible where it finds that the complaint has been fully and properly examined in convention terms by the domestic courts."

Legal experts were divided in their assessment. Philippe Sands, professor of international law at University College London, approved the final text. "The Brighton declaration will enhance the role of the ECHR, safeguard the vital right of individual petition, and help meet the challenge of the growing case-law," he said.

But Professor Philip Leach, a human rights specialist at London Metropolitan University, echoed Bratza's comments, saying: "It's a question as to whether there are enough specifics [left in the declaration] to make a real change. We have been discussing a lot of these issues for decades. The UK's attempt to change the admissibility criteria have been defeated, I'm glad to see. It's tinkering. There's no need to put a reference to the margin of appreciation [into the convention preamble]."

The human rights organisation Liberty welcomed the fact that the declaration "will omit various drastic proposals which would have undermined the right of individual petition, such as amending the convention to narrow the court of human rights' admissibility (HRA) criteria".

Isabella Sankey, Liberty's director of policy, said: "It's just a shame that politicians seem happy to talk up our strong implementation at the Council of Europe, yet so keen to try and scrap the HRA here at home."

Changes to the convention preamble will become effective following a routine meeting of foreign ministers from the 47 members states of the Council of Europe later this month.

Other changes contained in the declaration will require a fresh protocol to the convention that must be ratified by each of the member states. In the past, Russia has delayed ratification of similar reforms for several years.

Delegates were due to end their day's deliberations with a fish and chip supper on Brighton pier.